army1987 comments on Open Thread, April 15-30, 2013 - Less Wrong

4 Post author: diegocaleiro 15 April 2013 07:57PM

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Comment author: [deleted] 16 April 2013 07:50:24PM 0 points [-]

BTW, how comes the ring with one element isn't usually considered a field?

Comment author: Qiaochu_Yuan 16 April 2013 08:03:07PM 6 points [-]

The theorems work out nicer if you don't. A field should be a ring with exactly two ideals (the zero ideal and the unit deal), and the zero ring has one ideal.

Comment author: Oscar_Cunningham 16 April 2013 10:52:50PM *  2 points [-]

Ah, so it's for exactly the same reason that 1 isn't prime.

Comment author: Qiaochu_Yuan 17 April 2013 12:17:33AM 5 points [-]

Yes, more or less. On nLab this phenomenon is called too simple to be simple.

Comment author: Oscar_Cunningham 16 April 2013 10:51:39PM *  1 point [-]

We often want the field without zero to form a multiplicative group, and this isn't the case in the ring with one element (because the empty set lacks an identity and hence isn't a group). Indeed we could take the definition of a field to be

A ring such that the non-zero elements form a multiplicative group.

and this is fairly elegant.